Every program? DSPOBJD *ALL/*ALL *PGM
Use *ALLUSR/*ALL in order to omit IBM-supplied programs.
You’d probably want to add *SRVPGM and *MODULE objects too.
Every REXX procedure? Hmmm… you might have to create member lists of every source file on the system, then analyze every member to see if it contained any valid REXX at the beginning.
Every QShell and/or PASE script? I suppose that would be harder than REXX.
Every PASE binary executable? I figure they might have some kind of ‘signature’, but I sure don’t know what it would be. They probably at least will have the executable attribute set.
Windows and/or Linux executables in directories could be similar to PASE, but they possibly wouldn’t be considered for the list.

I might think of other possibilities with a little thought.

Any chance of being a little more specific on what the business objective is?